Polymer impurity removal method based on steam distillation
The present invention provides a method for depth removal of a volatile organic compound (VOC) in polymer resins and products thereof by means of a steam distillation method and apparatus thereof and significantly reducing the odor of the polymer resins and products thereof. The method provided in the present invention can further remove residual inorganic ash in the polymer resins. In the method, saturated steam at a certain temperature continuously keeps in contact with materials for a certain period of time, the VOC and an inorganic small molecule (ash) adsorbed on the surface of a polymer and wrapped inside the polymer are promoted to be enriched in a gas phase or a liquid phase and discharged, so as to reduce the VOC and ash in polymer materials, and the odor of the polymer resins or materials is decreased to a better level.
1 . A method for removing volatile organic compounds (VOC) in a polymer, reducing polymer odor, and removing inorganic ash, comprising the step of:
in a reaction system, continuously contacting water vapor, in a phase equilibrium state, with the polymer for 0.5-6 hours by:
(a) loading polymer in an equipment, wherein the equipment is a vertical or horizontal equipment;
(b) passing the water vapor, in the phase equilibrium state, through the equipment, continuously and directly contacting the polymer for 0.5-6 hours, while discharging the water vapor after contacting the polymer, wherein a temperature of the water vapor is 100-200° C.;
(c) dehydrating and drying the polymer; and
(d) discharging and collecting the dehydrated and dried polymer;
wherein the method removes volatile organic compounds (VOCs) and odor-forming components from the polymer by the continuous contacting of the polymer with the water vapor, so as to dissolve and remove the inorganic ash from the polymer; and
wherein during the contacting of the polymer with the water vapor, an oxygen content of the reaction system is lower than 0.1% (v/v).
2 . The method of claim 1 , further comprising:
in the reaction system and in step (b), continuously contacting the water vapor in the phase equilibrium state with the polymer for 0.5-3 hours.
3 . The method of claim 1 , wherein during the contacting of the polymer with the water vapor, the oxygen content of the reaction system is lower than 100 ppm.
4 . The method of claim 1 , further comprising:
before continuously contacting the water vapor in the phase equilibrium state with the polymer for 0.5-6 hours in the reaction system, the reaction system is first purged with an inert gas or water vapor to replace air in the reaction system.
5 . The method of claim 1 , further comprising:
continuously introducing water vapor into the reaction system while simultaneously discharging steam and/or condensed water; wherein a speed at which the steam is discharged is 1-200 Kg water vapor/ton polymer/hour.
6 . The method of claim 1 , wherein the polymer is selected from polyethylene (PE), polypropylene (PP), ethylene propylene rubber (EPDM, EPM), polyolefin elastomer (POE), polybutene PB-1, acrylonitrile/butadiene/styrene terpolymer (ABS), olefin block copolymer (OBC), nylon (PA), polycarbonate (PC), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene or polyphenylene sulfide, or a combination thereof.
7 . The method of claim 1 , wherein the polymer is polypropylene (PP) or polypropylene-random (PPR); and a melt flow index range of the polypropylene (PP) or polypropylene-random (PPR) is 0.1-2000 g/10 min measured according to GB/T 2682-2000.
8 . The method of claim 1 , wherein a temperature of the water vapor is about 20-50° C. 20-50° C. lower than a melting point of the polymer.
9 . The method of claim 1 , wherein:
when a particle diameter of the polymer is <1 mm and a VOC content in the polymer is <2000 ppm, a time for which the polymer is kept at a temperature corresponding to saturated water vapor is 0.5-3 h;
when the particle diameter of the polymer is <1 mm and the VOC content in the polymer is ≥2000 ppm, the time for which the polymer is kept at the temperature corresponding to saturated water vapor is 1-5 h;
when the particle diameter of the polymer is ≥1 mm and the VOC content in the polymer is <1000 ppm, the time for which the polymer is kept at the temperature corresponding to saturated water vapor is 1-5 h; or
when the particle diameter of the polymer is ≥1 mm and the VOC content in the polymer is ≥1000 ppm, the time for which the polymer is kept at the temperature corresponding to saturated water vapor is 3-7 h.
10 . The method of claim 1 , further comprising carrying out the method using the reaction system, wherein the reaction system comprises:
a steam stripping tower, wherein the equipment comprises the steam stripping tower;
a feed valve block located upstream of the steam stripping tower, the feed valve block is connected to a top feed port of the steam stripping tower, and is used to control entry of the polymer into the steam stripping tower; and
a discharge valve block located downstream of the steam stripping tower, the discharge valve block is used to control flow of the polymer out of the steam stripping tower;
optionally, wherein the reaction system further comprises:
a pre-dehydration tower located upstream of the feed valve block; and/or
a condenser wherein, an inlet of the condenser is connected with an exhaust outlet of the steam stripping tower, and an outlet of the condenser is connected with a condensate tank; and/or
a circulating water-cooling system wherein, the circulating water-cooling system is used to quench the polymer discharged from the steam stripping tower.
11 . The method of claim 10 , further comprising steps of:
(i) passing the polymer through the feed valve block and so that it enters the top feed port of the steam stripping tower;
(ii) passing steam through the steam stripping tower, and carrying out heat exchange with the polymer, so that an operating pressure inside the steam stripping tower corresponds to a saturated vapor pressure; and
(iii) discharging the polymer, wherein the discharge of the polymer is controlled by a rotary discharge valve block.
12 . The method of claim 1 , further comprising carrying out the method using the reaction system, wherein the reaction system comprises:
a micro negative pressure steam stripping tower, wherein the equipment comprises the micro negative pressure steam stripping tower;
a feed valve block located upstream of the micro negative pressure steam stripping tower, the feed valve block is connected to a top feed port of the micro negative pressure steam stripping tower, and is used to control entry of the polymer as a resin into the micro pressure steam stripping tower; and
a discharge valve block located downstream of the micro negative pressure steam stripping tower, the discharge valve block is used to control the flow of the resin out of the micro negative pressure steam stripping tower.
13 . The method of claim 12 , wherein the method further comprises:
(i) passing the polymer into the feed valve block, so that it enters the top feed port of the micro negative pressure steam stripping tower;
(ii) passing steam into water at a bottom of the micro negative pressure steam stripping tower, wherein a temperature in the micro negative steam stripping tower is controlled to generate steam and to carry out heat exchange with the resin which is an polyethylene or ethylene copolymer, so that the temperature of the polyethylene or ethylene copolymer is controlled at 50-95° C. to remove gas-phase impurity molecules;
(iii) operating the rotary discharge valve block to discharge the resin.
14 . The method of claim 1 , further comprising carrying out the method using the reaction system, wherein the reaction system comprises:
a wet nitrogen stripping tower, wherein the equipment comprises the wet nitrogen stripping tower;
a feed valve block located upstream of the wet nitrogen stripping tower, the feed valve block is connected to a top feed port of the wet nitrogen stripping tower, and is used to control the polymer in the form of a resin entering the wet nitrogen stripping tower;
a discharge valve block located downstream of the wet nitrogen stripping tower, the discharge valve block is used to control flow of the resin out of the wet nitrogen stripping tower;
a pre-dehydration tower located upstream of the feed valve block; and
a condenser, an inlet of the condenser is connected with an exhaust outlet of the wet nitrogen stripping tower, and an outlet of the condenser is connected with a condensate tank.
15 . The method of claim 14 , wherein the method comprises:
(1) passing the polymer in the form of a resin crude product into the top feed port of the wet nitrogen stripping tower through the feed valve block;
(2) passing wet nitrogen into the wet nitrogen stripping tower to carry out exchange heat with the crude resin product, and the crude resin product is heated to 50-95° C., so that VOC in the resin is desorpted;
(3) discharging the crude resin product, wherein the discharging is controlled through the discharge valve block.
16 . The method of claim 1 , further comprising carrying out the method using the reaction system, wherein the reaction system comprises:
a feed buffer tank, the feed buffer tank is used for temporarily storing the polymer, from which the VOC needs to be removed and the odor needs to be reduced;
a horizontal rotary furnace component, wherein the equipment comprises the horizontal rotary furnace component and; the horizontal rotary furnace component is located downstream of the feed buffer tank, and comprises a first horizontal rotary furnace and a second horizontal rotary furnace, and the horizontal rotary furnace component is a cascaded structure; and wherein the first horizontal rotary furnace and the second horizontal rotary furnace respectively have a material inlet, a steam inlet valve and an exhaust discharge valve.
17 . The method of claim 16 , the method further comprises:
(1) adding the polymer, from which the VOC needs to be removed and/or the odor needs to be reduced, into the feed buffer tank, wherein the first horizontal rotary furnace and the second horizontal rotary furnace are run, and steam is continuously injected into the horizontal rotary furnace component, while the material inlet is opened for feeding;
(2) keeping the polymer in the horizontal rotary furnace component, so that an azeotrope is formed from the VOC and the steam, and then opening the exhaust gas discharge valve to discharge the azeotrope from the horizontal rotary furnace component.
18 . The method of claim 10 , wherein the reaction system comprising the circulating water-cooling system, and the circulating water-cooling system comprises: a heat exchanger located downstream of the discharge valve block, and the heat exchanger is connected to a circulating water tank through a conveying pump; and/or
a Venturi feeder, wherein a first inlet of the Venturi feeder is connected with the discharge valve block, and a second inlet is connected with the heat exchanger.